After drilling on an oil or gas well is concluded there is often a buildup or accumulation of debris and contaminants adhered to the interior surface wall of the wellbore casing. If the wellbore casing is left unclean, debris and contaminates lining the casing wall could greatly throttle fluid flow and reduce well efficiency. Accumulated casing debris may also present dangerous well conditions by making wellbore repair more difficult, costly and time-intensive. Casing scrapers have been used for many years to clean and remove built-up debris from wellbore casing.
Traditional casing scrapers are connected directly with the drillstring and rotate axially with the rotation of the drillstring. These casing scrapers typically have radially extending scraper blades that rotate around the interior surface wall of the wellbore casing as the drillstring, rotates. As the drillstring is rotated in the wellbore, the scraper blades rotate at high speed against the interior casing wall and scrape away the buildup of accumulated debris left behind during the drilling process.
While these traditional casing scrapers are effective in vertical and near-vertical wellbores where the forces and pressures are relatively constant and well documented, these traditional rotating scrapers are much less effective and insufficient when the wellbore is deep or near horizontal like those wellbores that are now being drilled. In such deep wellbores and horizontal wellbores the frictional drag associated with rotating blade scrapers against the casing is unacceptable, as it greatly reduces the efficiency of the drillstring. These rotating scrapers can also cause long term wear and associated damage to the casing of the wellbore, reducing the life of the well and the costs associated with repair.
Non-rotating scrapers have been utilized to address the disadvantages associated with rotating casing scrapers. These devices utilize multiple components threadedly connected at smaller joints to form a larger mandrel. These threaded joints weaken the assembly and increase the risk of failures that may ultimately cause the scrapers to disconnect, shear, unthread, or break apart under the high torque encountered during use. The risk of failure of associated with such non-rotating casing scrapers will increase when such scrapers are used on long and near-horizontal wellbores such as wellbores 10,000 feet or longer now becoming common in the drilling of oil and gas wells.
A further disadvantage of current scraper assemblies is that the alignment and orientation of the scraper blades does not completely eliminate axial rotation of the scraping assembly as it passed through a wellbore. Current scraper assemblies feature helical shaped blades designed to chisel (or push) debris from the wellbore casing. Some assemblies have scraper blades oriented such that they form a larger helix of blades around a mandrel housing assembly. These helical shapes naturally generate rotational forces in the assembly as the assembly is passed through the wellbore with fluid and mud running past. These rotational forces translate into axial rotation within the scraper assembly, reducing the effectiveness of the non-rotating element of the assembly. Even slight rotation of a helical blade can cause un-scraped surfaces in the casing as the tool is advanced.
A further disadvantage of previous casing scraper assemblies is their inherent selection of either left-handed or right-handed drilling. These scraper assemblies rarely afford the flexibility rotating in both directions without altering the equipment. These scraper assemblies employ slanted grooves or angled cutting surfaces on the scraper blade biased towards one axial direction, which greatly reduces the effectiveness of the assembly when switched between drilling directions. Because of the orientation of the cutting blades and the shape of the blades on previous casing scraper devices, each known scraper assembly can handle only one-directional drilling. The inability of the scraper to transition between different drilling directions creates the need for companies to purchase additional equipment and ultimately increases the cost of drilling oil and gas wells while reducing equipment flexibility at drilling sites.